Recording density setting method and magnetic disk device

ABSTRACT

According to one embodiment, a recording density setting method includes performing first process and performing second process. The first process including recording and reading data on and from a disk medium of a magnetic disk device, and acquiring first information for setting the read data to satisfy a certain quality criterion. The first information represents a first shape of a first plurality of unit regions. Each of the a first plurality of unit regions is a recording region of a unit capacity. The second process includes acquiring second information representing a second shape of the first plurality of unit regions, and setting a recording density on the basis of the second information. The second shape is formed by adding margin regions having the same area to the first plurality of unit regions of the first shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.16/286,926 filed Feb. 27, 2019 and is based upon and claims the benefitof priority from Japanese Patent Application No. 2018-146058, filed onAug. 2, 2018; the entire contents of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a recording densitysetting method and a magnetic disk device.

BACKGROUND

There are demands for a disk medium to increase the density at whichdata is recorded thereon, in order to increase the capacity of amagnetic disk device.

A recording density is defined by, for example, a combination of alinear recording density and a track density. The quality of a magneticdisk device is affected by settings of the linear recording density andthe track density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of amagnetic disk device according to a first embodiment;

FIG. 2 is a diagram illustrating an example of a configuration of themagnetic disk device according to the first embodiment;

FIG. 3 is a diagram for illustrating a recording surface of a diskmedium 101 in the first embodiment;

FIG. 4 is a diagram for illustrating an example of data recording ineach zone 201 in the first embodiment;

FIG. 5 is an exemplary diagram for illustrating an areal margin of arecording region per bit in the first embodiment;

FIG. 6 is a flowchart for illustrating an overview process for decidinga recording density in the first embodiment;

FIG. 7 is a flowchart illustrating the operation of S101 in the firstembodiment in detail;

FIG. 8 is a flowchart illustrating the operation of S102 in the firstembodiment in detail;

FIG. 9 is a flowchart illustrating the operation of S303 in the firstembodiment in detail;

FIG. 10 is a diagram for illustrating the operation of S402 in the firstembodiment in detail; and

FIG. 11 is a diagram illustrating a system that executes a recordingdensity setting method of a second embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a recording density settingmethod includes performing first process and performing second process.The first process including recording and reading data on and from adisk medium of a magnetic disk device, and acquiring first informationfor setting the read data to satisfy a certain quality criterion. Thefirst information represents a first shape of a first plurality of unitregions. Each of the a first plurality of unit regions is a recordingregion of a unit capacity. The second process includes acquiring secondinformation representing a second shape of the first plurality of unitregions, and setting a recording density on the basis of the secondinformation. The second shape is formed by adding margin regions havingthe same area to the first plurality of unit regions of the first shape.

Exemplary embodiments of a recording density setting method and amagnetic disk device will be explained below in detail with reference tothe accompanying drawings. The present invention is not limited to thefollowing embodiments.

First Embodiment

FIGS. 1 and 2 are diagrams illustrating an example of the configurationof a magnetic disk device according to a first embodiment. FIG. 1illustrates the inside of a housing 100 of a magnetic disk device 1 witha top cover removed. As illustrated in FIG. 1, the magnetic disk device1 includes disk mediums 101 and magnetic heads 102 that read and writedata.

The disk medium 101 (a first disk medium 101) illustrated in FIG. 1 isone of two disk mediums 101, and the other disk medium (a second diskmedium 101 (see FIG. 2) is located on the back side (a far side inFIG. 1) of the first disk medium 101. In the present embodiment, thenumber of the disk mediums 101 is exemplified as two, but the number ofthe disk mediums 101 may be one or three or more.

The two disk mediums 101 are attached at a certain pitch along arotating shaft 103 of a spindle motor, and rotate integrally with therotating shaft 103 at the same rotation speed.

The magnetic heads 102 are each attached to a leading end of an arm 104.The arm 104 is driven by a voice coil motor (VCM) 105 and rotates withina set range around a shaft 106 in both positive and negative directions.By this operation, the magnetic head 102 moves on a broken line T and ispositioned on any of tracks of the disk medium 101 in the radialdirection. Total four sets of head units each including the magnetichead 102 and the arm 104 are mounted on the disk mediums 101, i.e., oneset each on the front surfaces and the back surfaces of the two diskmediums 101. The head units can be specified by a head number.

Specifically, each magnetic head 102 is mounted on a head slider 108 atthe edge of a suspension 107 placed at the leading end of the arm 104.The magnetic head 102 includes a read element and a write element, andthe read element scans and reads data from an intended surface of thedisk medium 101, and the writ element writes data onto the intendedsurface of the disk medium 101. In other words, the magnetic head 102accesses the recording surface of the disk medium 101. In the exampleillustrated in FIG. 1, the magnetic head 102 records and reads data ontoand from the front surface of the first disk medium 101.

In addition, the magnetic disk device 1 includes a ramp load mechanism109 that moves the magnetic head 102 away from the disk medium 101 forparking.

The magnetic disk device 1 includes a control circuit 20 (see FIG. 2)that controls the respective elements of the magnetic disk device 1, atthe bottom, i.e., on the far side in FIG. 1. The control circuit 20communicates with a host (not illustrated) via an interface such as aconnection pin, which is attached to the housing 100 of the magneticdisk device 1 for external connection, and controls the respectiveelements of the magnetic disk device 1 in response to commands from thehost.

FIG. 3 is a diagram for illustrating the recording surface of the diskmedium 101 of the first embodiment. The front surface and the backsurface of the disk medium 101 include recording surfaces 200. FIG. 3illustrates one of the front surface and the back surface of the diskmedium 101. The recording surfaces 200 are each divided into a pluralityof concentric zones 201 about the center of rotation of the disk medium101. For the sake of simplicity, the zones 201 are exemplified by threezones 201-1, 201-2, and 201-3 as illustrated in FIG. 3. The number ofzones 201 of a single recording surface 200 is not limited to three.

Each zone 201 includes concentric tracks about the center of rotation ofthe disk medium 101. Each track includes a plurality of consecutivesectors in a circumferential direction. Each sector has a magneticregion, and data is rewritable thereto. Each zone 201 may be identified,for example, by a combination of a head number of the magnetic head 102and a zone number.

FIG. 4 is a diagram for illustrating an example of data recording oneach zone 201 in the first embodiment. Data is recorded on each zone 201by shingled magnetic recording (SMR). SMR is a data recording techniquethat allows adjacent tracks to be layered on top of each other. It canbe seen from FIG. 4 that according to SMR, a track pitch (TP) isnarrower than a core width (WHw) of the write element of the magnetichead 102. SMR enables reduction in the track pitch and improvement inthe recording density.

FIG. 4 illustrates the respective tracks when data is recorded fromradially outside to inside the disk medium 101. The recording directionis not limited thereto. The recording may be performed from the insidetoward the outside of the disk medium 101.

The qualities of the disk medium 101 and the magnetic head 102 varydepending on manufacturing variations. According to the magnetic discdevice 1 of FIG. 2, the recording surfaces (front surface and backsurface) of the disk mediums 101 are accessed by the four correspondingmagnetic heads 10. Thus, at the same recording density set to all therecording surfaces, the recording quality varies depending on aposition. The variation in the recording quality appears as a variationin bit error rate. In view of this, the recording density is adjusted bydividing the entire recording surface into a plurality of partialregions and individually setting the recording density for each partialregion.

The zones 201 correspond to the partial regions for the recordingdensity adjustment. In other words, the recording density isindividually set or decided for the zones 201. Such setting, as dividingeach of the front surfaces and the back surfaces of the disk mediums 101and into the multiple zones 201 and setting the recording density foreach zone 201, is known as a zone constant angular velocity (CAV) mode.

The recording density is specified by a combination of the linearrecording density and the track density as described above. The linearrecording density refers to a recording density of the disk medium 101in the circumferential direction. The track density refers to arecording density of the disk medium 101 in the radial direction. Forexample, the linear recording density can be represented in unit of bitsper inch (BPI). For example, the track density can be represented inunit of tracks per inch (TPI). Units representing both densities are notlimited thereto.

In the first embodiment, the linear recording density and the trackdensity of each zone 201 are set on the basis of an areal margin of arecording region per bit on the disk medium 101. The areal margin refersto an amount found by multiplying a track pitch margin by a bit pitchand corresponds to the area of a margin region. The track pitch marginrefers to an amount found by subtracting a first track pitch from asecond track pitch. The first track pitch is a track pitch required toensure a minimum quality. The first track is referred to as a trackpitch limit. The second track pitch is a track pitch decided by a setvalue of the track density. The track pitch margin may also be referredto as a track density margin or a TPI margin.

FIG. 5 is an exemplary diagram for illustrating the areal margin of therecording region per bit in the first embodiment. For example, when thelinear recording density is set to 2525 kBPI, and the track density isset to 587 kTPI, the recording region per bit has a substantiallyrectangular shape (a rectangle 300) defined by a bit pitch of about 10.1nm and a track pitch of about 43.3 nm. When the track pitch limit is36.1 nm, the track pitch margin is about 7.2 nm (=43.3 nm−36.1 nm).Thus, the areal margin, that is, the area of the margin region indicatedby a rectangle 320 is about 72 nm² (=7.2 nm×10.1 nm).

In this specification, the recording region per bit is referred to as aunit region. A shape of a unit region including no areal margin, thatis, a shape for ensuring the minimum quality is referred to as a firstshape. A shape of a unit region set by adding a region (margin region)corresponding to the areal margin to the unit region of the first shapeis referred to as a second shape. In the example illustrated in FIG. 5,a rectangle 310 defined by the bit pitch and the track pitch limitcorresponds to the first shape, and the rectangle 300 defined by the bitpitch and the track pitch obtained by adding the track pitch margin tothe track pitch limit corresponds to the second shape.

In the first embodiment, the linear recording density and the trackdensity of each zone 201 are set such that the areal margins become asuniform as possible among the unit regions, and each areal margin is aslarge as possible. A method of setting the linear recording density andthe track density will be described later in detail.

FIG. 2 illustrates an example of the configuration of the controlcircuit 20 of the magnetic disk device 1 according to the firstembodiment. As illustrated in FIG. 2, the control circuit 20 includes apre-amplifier (PreAmp) 21, a read channel circuit (RDC) 22, a hard diskcontroller (HDC) 23, a digital signal processor (DSP) 24, a microprocessing unit (MPU) 25, and a memory 26.

The pre-amplifier 21 amplifies and outputs a signal read from the diskmedium 101 by the magnetic head 102 (read element), and supplies theamplified signal to the RDC 22. Further, the pre-amplifier 21 amplifiesa signal from the RDC 22 and supplies the amplified signal to themagnetic head 102 (write element).

The RDC 22 includes an error correction circuit (ECC) 27 that performsdata encoding and decoding for error correction. The RDC 22 encodes datato be recorded on the disk medium 101 by the ECC 27 and supplies theencoded data to the pre-amplifier 21 as a signal. Further, the RDC 22allows the ECC 27 to decode the signal read from the disk medium 101 andsupplied from the pre-amplifier 21 for error detection and correction.Then, the RDC 22 outputs the error-corrected signal to the HDC 23 asdigital data.

The data encoding and decoding for error correction by the ECC 27 is notlimited to a specific method. As one example, low density parity check(LDPC) may be employed. Data block size serving as unit of encoding anddecoding by the ECC 27 is not limited to a specific size. The ECC 27 mayperform encoding and decoding in unit of sectors or in unit of tracks.The ECC 27 may perform encoding/decoding both in units of sectors and inunits of tracks. The MPU 25 may perform either encoding or decoding forerror correction.

The DSP 24 controls the spindle motor and the VCM 105 to performpositioning control such as seeking and following. Specifically, the DSP24 performs the positioning control by obtaining and demodulating servoinformation from the signal from the RDC 22 and calculating a VCM drivecommand value according to an error between a position demodulated fromthe servo information and a target position.

The HDC 23 is connected to the host via a certain interface, andcommunicates with the host. A standard to which the interface conformsis not limited to a specific standard. The HDC 23 receives data from theRDC 22 and transfers the data to the host. Further, the HDC 23 receivesdata from the host and outputs the data to the RDC 22.

The MPU 25 analyzes a command received from the host by the HDC 23 tomonitor a state of the magnetic disk device 1 and control the respectiveelements of the magnetic disk device 1.

The memory 26 is a data rewritable storage device. The memory 26functions as a storage region for programs and various kinds ofmanagement information used for various kinds of processing executed bythe MPU 25, a buffer region, and a cache region, for example. The memory26 includes a volatile memory, a non-volatile memory, or a combinationthereof. The volatile memory may be, for example, a static random accessmemory (SRAM) or a dynamic random access memory (DRAM). The non-volatilememory may be a flash memory.

In the first embodiment, the memory 26 stores a recording densitysetting program 261 for setting the recording density. The MPU 25executes the recording density setting program 261 stored in the memory26 to set the recording density (that is, a pair of the set value of thelinear recording density and the set value of the track density) foreach zone 201.

The set recording density for each zone 201 is stored in a non-volatilememory region of the magnetic disk device 1. After shipment of themagnetic disk device 1, the control circuit 20 controls access to thedisk medium 101 in accordance with the recording density of each zone201 stored in the non-volatile memory region.

The non-volatile memory region in which the set recording density foreach zone 201 is stored is not limited to a specific region. Forexample, it may be a non-volatile memory of the memory 26 or a certainregion on the disk medium 101. For example, the disk medium 101 mayinclude a conventional magnetic recording (CMR) region in which data isrecorded by CMR so as to avoid tracks from overlapping, to store the setrecording density for each zone 201 in the CMR region.

After the recording density is set, the recording density settingprogram 261 may be or may not be deleted from the memory 26.

FIG. 6 is a flowchart for describing an overview of a recording densitysetting process of the first embodiment.

First, the MPU 25 acquires a pair of linear recording density and trackpitch limit as information on the first shape (first information)(S101).

A plurality of values of the linear recording density covering asettable range is prepared in advance. In S101, the MPU 25 measures thetrack pitch limit for each of the plurality of values of the linearrecording density.

In S101, the MPU 25 measures the track pitch limit for each value of thelinear recording density in each zone 201. In other words, the firstinformation represents information containing a pair (a pair of linearrecording density and track pitch limit) for each value of the linearrecording density and for each zone 201.

FIG. 7 is a flowchart illustrating the operation in S101 in detail inthe first embodiment.

First, the MPU 25 initializes to zero a head number HEAD being an ID ofthe magnetic head 102 and a zone number ZONE being an ID of each zone201 of each recording surface 200 (S201). In one example of theprocessing in FIG. 7, the zone 201 specified by a combination of thehead number HEAD and the zone number ZONE is referred to as a targetzone 201.

Then, the MPU 25 initializes a loop counter j to 1 (S202). The MPU 25initializes a length parameter d to an initial value dini (S203). Theinitial value dini is preset, for example.

As an example, n values (DL1, DL2, . . . , DLn), which cover a settablelinear recording density range, of the linear recording density areprepared in advance. The MPU 25 selects a value DLj from the values DL1to DLn and records data of one track (referred to as a target track) inthe target zone 201 while controlling the linear recording density toDLj (S204). The magnetic head 102 specified by the head number HEAD isused for recording the data in the target zone 201.

Then, the MPU 25 records data of another track (referred to as anadjacent track) at a location adjacent to the target track (S205). InS205, the MPU 25 records the data of the adjacent track so that thetrack pitch TP of the target track is equal to d.

Specifically, the MPU 25 controls the radial position of the magnetichead 102 specified by the head number HEAD to a position radially offsetfrom the position in S204 by d, and executes the operation in S205. Indata recording from inside to outside of the disk medium 101, the MPU 25shifts the position of the magnetic head 102 outward. In data recordingfrom outside to inside the disk medium 101, the MPU 25 shifts theposition of the magnetic head 102 inward. Thereby, the track pitch TP ofthe target track can be made equal to d.

In S205, the MPU 25 also controls the linear recording density to DLjfor the recording.

Then, the MPU 25 reads data from the target track and measures a sectorerror rate at the time of the data reading (S206).

The sector error rate refers to the number of bit errors in each sector.A method of measuring the sector error rate is not limited to a specificmethod. For example, the MPU 25 may control the ECC 27 to report thesector error rate when data is read.

Then, the MPU 25 determines whether or not the measured sector errorrate is equal to a reference value (S207). The reference valuecorresponds to a minimum quality. In other words, in S207, the MPU 25determines whether or not the quality of the data recorded in the targettrack and read therefrom satisfies a certain criterion. The sector errorrate equal to the reference value is an example that the quality of thedata recorded and read from the target track satisfies a certaincriterion.

The reference value is set, for example, in accordance with errorcorrectability of the ECC 27. If the sector error rate is less than orequal to a certain value, the error correction always succeeds, but ifthe sector error rate exceeds the value, success of the error correctioncannot be ensured, the reference value is set to the certain value. Amethod of setting the reference value is not limited thereto.

When the sector error rate is not equal to the reference value (NO inS207), the MPU 25 determines whether or not the sector error rate issmaller than the reference value (S208).

When the sector error rate is smaller than the reference value (YES inS208), the MPU 25 increases the value of d by a certain step width dstep(S209). When the sector error rate is not smaller, i.e., larger than thereference value (NO in S208), the MPU 25 decreases the value of d by thecertain step width dstep (S210).

A method of increasing and decreasing the value of d in S209 and S210 isnot limited thereto. The MPU 25 may change the value of d by anarbitrary method.

After S209 or S210, the MPU 25 newly sets the adjacent track recorded inS204 as the target track (S211), and returns to S205.

When the sector error rate is equal to the reference value (YES inS207), the MPU 25 sets a current value of d as the track pitch limit forthe linear recording density being DLj (S212).

The track pitch limit for the linear recording density being DLj isrepresented by minTP(DLj). At the linear recording density of DLj, thefirst shape is defined by minTP(DLj) and the bit pitch BPj at the timeof the linear recording density of DLj. The bit pitch BPj at the linearrecording density being DLj can be found by calculating a reciprocal ofDLj. In other words, a pair of DLj and minTP(DLj) represents the firstshape at the linear recording density of DLj, and corresponds to thefirst-shape information.

A representation of the first-shape information is not limited thereto.Any information from which the first shape can be derived can beemployed as the first shape-information. For example, a combination ofthe linear recording density and the track density, a combination of thebit pitch and the track density, or a combination of the bit pitch andthe track pitch can be employed as the first-shape information.

The MPU 25 stores a pair of DLj and minTP(DLj) in a certain memoryregion (for example, a temporary data region of the memory 26) inassociation with the target zone 201 (S213).

In S207, the MPU 25 may determine that the sector error rate is equal tothe reference value, even if the sector error rate does not coincidewith the reference value. For example, the MPU 25 may determine that thesector error rate is equal to the reference value if the sector errorrate falls within a certain range including the reference value.

Subsequently to S213, the MPU 25 increments j by 1 (S214). Then, the MPU25 determines whether or not the value of j exceeds n (S215).

The letter n represents the number of the values DL1 to DLn of thelinear recording density which are prepared in advance. In the case ofusing all of DL1 to DLn, the value of j exceeds the number n (YES inS215). In this case, the MPU 25 increments the zone number ZONE by 1 anddetermines whether or not the zone number ZONE exceeds a maximum valuemaxZONE of the zone number (S216).

When the zone number ZONE does not exceed maxZONE (NO in S216), the MPU25 returns to S203.

When the zone number ZONE exceeds maxZONE (YES in S216), the MPU 25increments the head number HEAD by 1 and determines whether or not thehead number HEAD exceeds a maximum value maxHEAD of the head number(S217).

If the head number HEAD does not exceed maxHEAD (NO in S217), the MPU 25initializes the zone number ZONE to zero (S218), and returns to S202.

When the head number HEAD exceeds maxHEAD (YES in S217), the operationin S101 ends.

As described above, when the sector error rate is less than thereference value, the MPU 25 re-executes recording and reading at anarrowed track pitch, searching for the track pitch (track pitch limit)at which the sector error rate becomes equal to the reference value.When the sector error rate exceeds the reference value, the MPU 25re-executes recording and reading at a widened track pitch, searchingfor the track pitch limit.

The MPU 25 acquires the track pitch limit for each zone and for eachcandidate value of the linear recording density. Thus, through theseries of operations illustrated in FIG. 7, the MPU 25 can acquire, asfirst information, the first-shape information (a pair of linearrecording density and track pitch limit) for each of the n linearrecording densities DL1 to DLn in each zone 201.

Returning to FIG. 6, after S101, the MPU 25 sets the value of therecording density on the basis of information (second information) onthe second shape which is formed by adding the same areal margin to eachunit region of the first shape (S102).

FIG. 8 is a flowchart illustrating the operation in S102 in detail inthe first embodiment.

First, the MPU 25 initializes a parameter AM indicating a candidatevalue of the areal margin to an initial value AMini (S301). Then, theMPU 25 initializes the head number HEAD and the zone number ZONE to zero(S302). In one example of the processing in FIG. 8, the zone 201specified by the head number HEAD and the zone number ZONE is referredto as a target zone 201.

Subsequently to S302, the MPU 25 acquires a combination of the trackdensity and the linear recording density for the target zone 201 inwhich the recording density of the target zone 201, when the marginregion of the area margin AM is assumed to be added to each unit regionof the first shape, becomes to a maximum value (S303).

FIG. 9 is a flowchart illustrating the operation in S303 in detail inthe first embodiment.

First, the MPU 25 initializes the loop counter j to 1 (S401). Then, theMPU 25 acquires the track pitch limit minTP(DLj) at the linear recordingdensity being DLj from the first information obtained by the processingFIG. 7. Then the MPU 25 calculates the track density DTj in which theareal margin AM is assumed to be added to the unit region of the firstshape indicated by a pair of DLj and minTP(DLj)(S402). In S402, the MPU25 acquires the track pitch limit minTP(DLj) of the target zone 201.

FIG. 10 is a diagram for illustrating the operation in S402 in detail inthe first embodiment.

In FIG. 10, a rectangle 400 represents the first shape defined by thetrack pitch limit minTP(DLj) and the bit pitch BPj corresponding to thelinear recording density DLj. The areal margin AM is added to therectangle 400 in the radial direction of the disk medium 101. In otherwords, the second shape is a rectangle 420 created by radially extendingthe rectangle 400 by a length (denoted by dTP) corresponding to the areaof AM.

An extended, added region 410 corresponds to the margin region, and thearea of the region 410 is AM. Thus, the length dTP can be expressed bythe following Formula (1):

dTP=AM/BPj.

The track pitch TPj of the second shape can be expressed by thefollowing Formula (2):

TPj=minTP(DLj)+AM/BPj

The MPU 25 can find the track density DTj for the unit region of thefirst shape including the added areal margin AM, indicated by a pair ofDLj and minTP(DLj), by calculating a reciprocal of the track pitch TPjfound by Formula (2).

The rectangle 420 as the second shape is defined by a pair of bit pitchBPj and track pitch TPj. That is, the pair of the linear recordingdensity DLj corresponding to the reciprocal of the bit pitch BPj and thetrack density DTj corresponding to the reciprocal of the track pitch TPjrepresents information on the rectangle 420 being the second shape.

In other words, the operation of S402 corresponds to acquiring thesecond-shape information at the areal margin being AM and the linearrecording density being DLj.

The representation of the second-shape information is not limitedthereto. Any information from which the second shape can be derived canbe employed as the second-shape information. For example, a combinationof the linear recording density and the track pitch, a combination ofthe bit pitch and the track density, or a combination of the bit pitchand the track pitch can be employed as the second-shape information.

Returning to FIG. 9, after S402, the MPU 25 increments j by 1 (S403).Then, the MPU 25 determines whether or not the value of j exceeds n(S404).

When the value of j does not exceed n (NO in S404), the MPU 25 returnsto S402. When the value of j exceeds n (YES in S404), the MPU 25selects, among the acquired combinations of the linear recording densityDLi (where i is an integer of 1 to n) and the track density DTiacquired, a combination at which the recording density (a product of thetrack density and the linear recording density) for the target zone 201becomes to be the maximum (S405). This completes the operation of S303.

As described above, the MPU 25 calculates the recording density for thetarget zone 201 in which the areal margin AM is added to each firstshape, to thereby acquire a combination of the linear recording densityand the track density to maximize the recording density.

Returning to FIG. 8, after S303, the MPU 25 stores the pair of the trackdensity and the linear recording density acquired in S303 in a certainmemory region (for example, a temporary data region of the memory 26) inassociation with the target zone 201 (S304). Then, the MPU 25 calculatesthe capacity of the target zone 201 at the pair of the track density andthe linear recording density acquired in S303 (S305).

The MPU 25 increments the zone number ZONE by 1 and determines whetheror not the zone number ZONE exceeds the maximum value maxZONE of thezone number (S306).

When the zone number ZONE does not exceed maxZONE (NO in S306), the MPU25 returns to S303.

When zone number ZONE exceeds maxZONE (YES in S306), the MPU 25increments the head number HEAD by 1 and determines whether or not thehead number HEAD exceeds the maximum value maxHEAD of the head number(S307).

When the head number HEAD does not exceed maxHEAD (NO in S307), the MPU25 initializes the zone number ZONE to zero (S308), and the MPU 25returns to S303.

When the head number HEAD exceeds the maxHEAD (YES in S307), the MPU 25calculates a total capacity of the respective zones 201 (S309).

The MPU 25 determines whether or not the total capacity coincides with auser capacity (S310). When the total capacity is equal to the usercapacity (YES in S310), the MPU 25 sets the pair of the linear recordingdensity and the track density of each zone 201 stored in S304 as valuesof a pair of linear recording density and track density of each zone 201(S311), ending the operation of S102.

When the total capacity is not equal to the user capacity (NO in S310),the MPU 25 clears the pair of linear recording density and track densityof each zone 201 stored in S304 (S312), and determines whether or notthe total capacity is larger than the user capacity (S313). When thetotal capacity is larger than the user capacity (YES in S313), the MPU25 reduces AM by a certain step width AMstep (S314), and returns to theprocess of S302. In other words, the MPU 25 reduces the areal margin,and adjusts the pair of linear recording density and track densityagain.

When the total capacity is not larger i.e., smaller than the usercapacity (NO in S313), the MPU 25 increases AM by a certain step widthdelta (S315), and returns to S302. Thus, the MPU 25 adjusts the pair ofthe linear recording density and the track density again with theincreased areal margin.

In S310, the MPU 25 may determine that the total capacity is equal tothe user capacity, even if the total capacity does not coincide with theuser capacity. For example, the MPU 25 may determine that the totalcapacity is equal to the user capacity as long as the total capacityexceeds the user capacity and a difference between them is equal to orless than a certain value.

As described above, the recording density setting method of the firstembodiment includes a first step (for example, S101) and a second step(for example, S102). In the first step, data is recorded on and readfrom the disk medium 101 (for example, S204 to S206), and the firstinformation representing the first shape of the first unit regions, isacquired for setting the read data to satisfy a certain qualitycriterion (for example, S212 and S213). The first unit regions arerecording regions of a unit capacity. In the second step, the secondinformation representing the second shape, which is formed by adding thesame area margin AMs to each unit region of the first shape, is acquired(for example, S304), to set the recording density on the basis of thesecond information (for example, S311).

A first example and a second example will be described for the purposeof comparison with the first embodiment. In the first example, the shapeof the unit regions is set so that the bit error rate of the magneticdisk device becomes uniform and lowest. According to the second example,the shape of the unit regions is set so that the track pitch margin ofthe magnetic disk device becomes uniform and maximum.

However, the first example cannot ensure tolerance to overwriting,particularly, in the case of SMR data recording. The second examplecannot ensure the margin of the bit error rate relative to the variationin the recording quality.

According to the recording density setting method of the firstembodiment, the same areal margin is added to the first unit regions onthe basis of the shape (first shape) that can ensure a minimum quality.In other words, the recording density is set so that the first unitregions include the same areal margin.

The areal margin is represented by a product of the bit pitch and thetrack pitch margin. It is thus possible to provide a high-qualitymagnetic disk device 1 which can ensure both the tolerance to theoverwriting and the margin of the bit error rate in a balanced manner.In other words, according to the first embodiment, the quality of themagnetic disk device 1 can be improved.

The first unit regions are, for example, all the unit regions of themagnetic disk device 1. It is thus possible to make the areal margins ofall the unit regions of the magnetic disk device 1 uniform. The firstunit regions may be part of the unit regions of the magnetic disk device1. For example, the first unit regions may be all the unit regions ofpart of all the zones 201 of the magnetic disk device 1. In this case,the areal margins of the part of the zones 201 can be made uniform.

In the above explanation, the recording region per bit is defined as theunit region. The definition of the unit region is not limited thereto. Arecording region per two or more bits may be defined as the unit region.

Further, the second shape (for example, the rectangle 420 in FIG. 10) iscreated by extending the first shape (for example, the rectangle 400 inFIG. 10) in the radial direction of the disk medium 101 by the lengthcorresponding to the areal margin AM.

The extended length corresponding to the areal margin AM serves as thetrack pitch margin. This can ensure the tolerance to the overwriting.

Further, the recording surfaces 200 of the disk medium 101 include thepartial regions (for example, zones 201) each including unit regions.The first step includes acquiring the first shape for each partialregion (for example, S201 to S215). The second step includes setting therecording density for each partial region (for example, S311).

Thus, the area margins of all the unit regions of the partial regionscan be made uniform irrespective of different first shapes in thepartial regions. This makes it possible to provide a magnetic diskdevice 1 in which the areal margin of the unit regions of one of twopartial regions is made equal to that of the unit region of the otherpartial region, for example.

Further, the second step includes calculating the total capacities ofthe disk medium 101 while changing the areal margin (for example, S312to S315 and S309), and setting the recording density on the basis of thetotal capacities and the user capacity of the magnetic disk device 1(for example, S310 and S311).

This makes it possible to optimize the areal margin in accordance withthe user capacity.

Further, when a largest total capacity not exceeding the user capacityamong the total capacities is calculated, the recording density is seton the basis of the second shape corresponding to the largest totalcapacity (for example, S310 and S311).

Thus, the areal margin is maximized, and as a result, both the toleranceto the overwriting and the margin of the bit error rate to be balancedare achieved in a highly balanced manner.

The first step further includes acquiring first shapes having differentratios of the track pitch and the bit pitch. For example, as illustratedin FIG. 7, the values (DL1 to DLn) of the linear recording density areprepared in advance, to calculate the track pitch limit minTP for eachvalue of the linear recording density. Thereby, the first shapes havingdifferent ratios of the track pitch and the bit pitch are acquired. Inthe second step, a first shape having the maximum recording density(that is, the product of the track density and the linear recordingdensity) among the first shapes is acquired each time the candidate ofthe areal margin is changed (for example, S303 and S401 to S406), tocalculate the total capacity on the basis of the acquired shapes (forexample, S309).

Thus, it is possible to equalize and maximize the areal margins.

In the first step, the sector error rate is measured as an indexrepresenting the quality (for example, S206), to acquire the shape ofthe unit region having the measured sector error rate of a certain value(for example, S207, S212, and S213).

It is therefore possible to acquire the shape of the unit region forensuring the minimum quality.

The sector error rate refers to the bit error rate per sector. A unit ofthe bit error rate measurement is not limited to sector alone. Forexample, the bit error rate per track may be measured.

According to the first embodiment, the magnetic disk device 1 recordsdata by SMR by way of example. By SMR, the recording density can beimproved by narrowing the track pitch than the width WHw of therecording element of the magnetic head 102. According to the firstembodiment, the track pitch can be set with the margin up to the trackpitch limit, which can ensure the minimum recording quality even in thesituation that the magnetic head 102 is unintentionally offset inposition during SMR recording.

The magnetic disk devices to which the technique of the first embodimentcan be applied are not limited to the SMR recording devices. Thetechnique of the first embodiment can also be applied to devices whichrecord data in accordance with CMR or both SMR and CMR.

In the above description, the linear recording density and the trackdensity of each zone 201 are set so as to equalize and enlarge the arealmargins in the entire recording surfaces 200 as much as possible. Inorder to achieve uniform and constant recording quality on the entirerecording surfaces 200, ideally, the areal margin is to be uniform andmaximal in the entire recording surfaces 200. However, if larger qualitydeterioration is anticipated in a portion, indicated by a specificmagnetic head 102, a specific zone 201, or a combination of the two,than in the rest of the recording surfaces 200, the areal margin doesnot need to be uniformly distributed. The areal margin may beproportionally distributed depending on a difference in the qualitydeterioration.

Examples of the factors of the difference in the quality deteriorationinclude differences in the parts of the respective elements such aspositioning accuracy when applied with vibration or impact, jittercaused by a difference in recording frequency, and amount ofdeterioration in a thermal fluctuation quality caused by non-uniformmagnetic characteristics of the disk mediums 101. The factors of thedifference in the quality deterioration are not limited thereto.

Upon selecting a specific zone 201 as the target zone 201, for example,the MPU 25 can distribute the areal margin by temporarily adjusting theareal margin AM immediately before S303. For another example, the MPU 25can adjust the areal margin AM by adding a certain amount to the arealmargin AM or multiplying the areal margin AM by a certain number. Adistribution method of the areal margin is not limited thereto.

Second Embodiment

The first embodiment has described the example in which the MPU 25 ofthe magnetic disk device 1 sets the recording density. Alternatively,the magnetic disk device 1 may incorporate a dedicated hardware circuitthat sets the recording density. The MPU 25 may decide the recordingdensity in cooperation with the hardware circuit.

Alternatively, as illustrated in FIG. 11, for example, the magnetic diskdevice 1 may be connected to an external device 300, and the externaldevice 300 may control the hardware of the magnetic disk device 1 to setthe recording density.

For example, the external device 300 represents a computer including aprocessor 30 and a memory 31. The recording density setting program 32is stored in the memory 31 in advance. The processor 30 executes therecording density setting program 32 to set the recording density. Theprocessor 30 sequentially transmits commands to the magnetic disk device1 and implements the respective processes illustrated in FIGS. 7 to 9.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk device, comprising: a disk mediumincluding a first partial region and a second partial region, each ofthe first and second partial regions including a plurality of unitregions each of which is a recording region of a unit capacity, whereinan area of the margin region of an unit region in the first partialregion is equal to an area of the margin region of an unit region in thesecond partial region.
 2. The magnetic disk device according to claim 1,wherein the unit capacity is a capacity of 1 bit, a track pitch and abit are set for each of the first and second partial regions, the areaof the margin region of the unit region in the first partial regioncorresponds to a value obtained by multiplying a first value by a secondvalue, the first value being a bit pitch set for the first partialregion, the second value being a value obtained by subtracting a thirdvalue from a fourth value, the third value being a value of a trackpitch to make a sector error rate at a time of reading data that isrecorded with a bit pitch of the first value in the first partialregion, the fourth value being a track pitch set for the first partialregion, the area of the margin region of the unit region in the secondpartial region corresponds to a value obtained by multiplying a sixthvalue by a seventh value, the sixth value being a bit pitch set for thesecond partial region, the seventh value being a value obtained bysubtracting an eighth value from a ninth value, the eighth value being avalue of a track pitch to make a sector error rate at a time of readingdata that is recorded with a bit pitch of the sixth value in the secondpartial region, the ninth value being a track pitch set for the secondpartial region.
 3. The magnetic disk device according to claim 1 furthercomprising a magnetic head, wherein the magnetic head records data intothe first and second partial regions by shingled magnetic recording. 4.The magnetic disk device according to claim 1, wherein the disk mediumhas a recording surface, the recording surface is divided into aplurality of partial regions in a radial direction of the disk medium,the first partial region is one of the plurality of partial regions, andthe second partial region is another of the plurality of partialregions.
 5. A magnetic disk device, comprising: a disk medium includingpartial regions, each of the partial regions including a plurality ofunit regions each of which is a recording region of a unit capacity,wherein an area of the margin region of an unit region in each partialregion is uniform for all of the partial regions.
 6. The magnetic diskdevice according to claim 5, wherein the unit capacity is a capacity of1 bit, a track pitch and a bit are set for each of the partial regions,the area of the margin region corresponds to a value obtained bymultiplying a first value by a second value, the first value being a setvalue of a bit pitch, the second value being a value obtained bysubtracting a third value from a fourth value, the third value being avalue of a track pitch to make a sector error rate at a time of readingdata that is recorded with a bit pitch of the first value, the fourthvalue being a set value of a track pitch.
 7. The magnetic disk deviceaccording to claim 6 further comprising a magnetic head, wherein themagnetic head records data into each of the part